[TUDOR]

Now, since MTD was not forthcoming with what RPM the blower requires at input, the answer to the question of whether I'm running the blower at sufficient speed or not may have to remain a mystery.

However, do any of you out there with similar sized blower attachments have any RPM readings on your impeller that I can compare to? Are they significantly higher than 1400 RPM? I'd be interested to hear feedback on this.

Great read!!

For a better answer, try impeller tip speed. There are several different diameter impellers, but the tip speeds should all be close. The tip speed and width of the impeller will determine the hp requirement.

MTD may not be forthcoming, but most smaller 3ph blower impellers run at 540 rpm and tip speeds of 2400- 3000 ft/min. ( Circumference x rpm )

 

[TUDOR]

Ok I went out and measured.. my impeller blades are about 6" long, so..

Circumference = 2 x pi x r
Tip speed = Circ. x RPM = 2 x 3.14 x 0.5 x 1400 = 4400 ft/min.

Hmm, certainly seems high enough. I guess what occurs to me now is all these measurements are being done at no load. Maybe when the blower is loaded down I may be getting less RPM than I'm supposed to, possibly due to belt slippage (the engine RPM is governed and doesn't change under load).


By the way, I finished (at least in the rough) my electric blower lift mod just in time to use the blower again last night.. we had a good 6" of snow on the ground. Worked great, but then again it wasn't particularly heavy snow.

For that info I just searched for 3PH blowers and took the tip speeds from the smaller ones. IIRC the tip speed for my Pronovost 48" blower with a 16" fan was 5000 fpm @ 3600 engine rpm. That would throw chunks of ice 80' at a relatively low departure angle and snow would go across my front lawn into the neighbour's driveway at a similar angle. That is not really conducive to city life and obstacles or good neighbour relations. That blower has been sitting unused for 21 years, but might get refurbished and detuned for next winter to augment my 2 FELs.

It's been many years since I did those calculations so I didn't want to tax my memory when the info for 3PH blowers was immediately available. I'm still not positive that my calculations for the Pronovost are right.

 

[TUDOR]

And using your formula above (same impeller radius) the 2000rpm equals 6280 ft/min, snow may end up in the next county.

The tip speed of the impellor of my blower is about 5000 fpm at 2000 rpm PTO speed, enough to blow the snow across my 40' lawn and into my neighbour's driveway with the chute at a relatively low angle. He was in the process of blowing his driveway at the time and wasn't happy until I told him that I would clean his driveway after I finished mine. When the grader scraped the hard pack off the road one day, I was blowing chunks far enough to bounce them off his front door 80' away, again at a relatively low chute angle since I have aluminum siding.

I wouldn't recommend a tip speed over 6000 fpm unless there is lots of space in the direction that the snow is being directed. The higher tip speed is also going to require considerably more horsepower for the same travel speed.

Most GT blowers have an impellor tip speed between 4000 and 4800 fpm.